An assessment of the available thermodynamic data of gaseous and condensed fullerene C 70 is presented. Gibbs energy minimization of the gaseous C-H-O-Ar chemical system, including large polyaromatic hydrocarbons and the fullerenes C 60 and C 70 , helps to determine under which conditions C 60 and C 70 molecules are stable. The influence of the addition of halogen atoms in the gas phase on the improvement of the yield of these two fullerenes in different conditions is investigated by minimizing the Gibbs energy of the gaseous C-H-F-O-Ar chemical system. The evolution of the yields of the two fullerenes, and of the C 70 /(C 70 ϩ C 60 ) ratio as a function of temperature, pressure, and C/H ratio in the reactants is illustrated and compared with corresponding experimental information from a literature review. In the light of these calculations, the possibility of the direct production of fullerene films containing variable amounts of C 60 and C 70 by a continuous process such as combustion or pyrolysis is discussed.

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